The inhomogeneous Ba0.7Sr0.3TiO2 thin films characterized by Ba/Sr ratio fluctuation in micro-region hold the P-E hysteresis loop from low temperature to 150 degree(s)C, which is higher than the upper limited Curie temperature of Ba1-xSrxTiO3 (BST) solid solutions. The fluctuation of Ba/Sr ratio in sub-micron scope results in abnormal ferroelectric behavior for BST thin films. We suggest that this phenomenon can be explained by the internal stress effect caused by lattice mismatch in the inhomogeneous BST thin films. The inhomogeneity of the thin film was simulated according to the Gaussian distribution and the internal stress was calculated. The simulated results show that three kinds of typical stressed micro-regions exist in the inhomogeneous film. Especially, the Ba-rich micro-regions are compressed biaxially in film plane, which tends to promote the polarization normal to the film plane and so ferroelectricity of the Ba-rich micro- regions keeps to higher temperature. The internal stress model is reasonable to explain the ferroelectric abnormality of the thin films.